Rubidium has two naturally occurring isotopes.The atomic weight of Rb is 85.4678 u.If 72.15% of Rb is found as Rb-85 (84.9117 u),what is the mass of the other isotope?
A) 0.56 u
B) 85.68 u
C) 86.68 u
D) 86.02 u
E) 83.47 u

Question

Quizplus · Accepted Answer

To find the mass of the other isotope, use the formula for average atomic mass: (0.7215 * 84.9117 u) + (0.2785 * x) = 85.4678 u. Solving for x gives approximately 86.68 u.

Rubidium Has Two Naturally Occurring Isotopes